The present invention relates to water flow monitors in general and in particular to flow monitors employing a turbine.
Measuring the flow of a fluid in a pipe can be difficult, depending on the level of accuracy required. A positive displacement pump is probably the most accurate conventional approach; however, such pumps are costly, cause a significant pressure drop and are relatively bulky. Simple paddlewheel type sensors may be of low-cost and have little resistance to the flow of fluid, but may suffer from a lack of accuracy over a wide range of fluid flow rates, particularly at low or very high flow rates.
Precision flow instruments employ a turbine that passes substantially all the flow. However, bearing friction can seriously impede accuracy at higher flow velocities. The typical solution is to over-design the bearings which support the flow turbine, with the result being a relatively expensive instrument not suitable for use in many commercial and consumer applications, such as boilers, shower pumps, and tank filling applications. Flow monitoring with relative precision is necessary for residential and commercial water meters. Flow monitoring can also detect problems within waterflow systems, and can allow modulation of water flow velocities with greater precision. Flow monitoring can be important in hot water heating systems where monitoring flow assures balanced heating. Flow monitoring can also be used to increase energy efficiency by, for example coordinating water flow with burner activation in a boiler. Monitoring of fluid flow through a pump can assure that adequate fluid flows are present for pump cooling and avoiding cavitation at the pump impeller.
What is needed is a turbine type flow monitor that is low-cost, relatively accurate, creates a relatively low-pressure drop, and is resistant to leaks.
The turbine type flow meter of the present invention has an in-line housing in which a four-vaned torpedo-shaped turbine is between a first bearing spaced along the axis of flow from a second bearing. The bearings are supported by a plurality of axially extending spokes. The turbine supports a pair of magnets that rotate with the turbine. An upstream portion of the housing incorporates a sensor cavity that is sealed from a flow cavity formed by the flow meter. The sensor cavity is closely spaced from the rotating magnets positioned on the turbine. Positioned within the sensor cavity is a printed circuit board on which a Hall effect sensor is mounted. A connector mounted to the circuit board extends from the sensor cavity. The circuit board is mounted within the sensor cavity so that the Hall effect sensor is positioned close to the rotating magnets of the turbine. A temperature sensor may also be mounted on the circuit board and the circuit board may be potted within the sensor cavity with polyurethane or epoxy.
The sensor housing is constructed from two parts: a first upstream part containing the sensor cavity, and a second downstream part containing the downstream bearing. Both the upstream part of the housing and the downstream part of the housing incorporate pipe fittings to allow the turbine housing to be readily positioned along a fluid flow pipe. The upstream housing and the downstream housing incorporate mating structures that are designed for joining by spin welding.
It is a feature of the present invention to provide a fluid flow sensor of low cost.
It is a further feature of the present invention to provide a fluid flow sensor, which monitors fluid temperature in addition to fluid flow rate.
It is a still further feature of the present invention to provide a fluid flow sensor, which is accurate at low fluid velocities.
It is a yet further feature of the present invention to provide a fluid flow sensor, which occupies little additional volume beyond the volume, occupied by the fluid piping.
Further features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.